The present invention pertains to a safety locking device for use with the gear shifting mechanism of an industrial truck, such as a fork lift, so that the transmission is locked against shifting gears until the vehicle's brakes are applied.
One of the characteristics of the typical fork lift vehicle is that the gears can be shifted from forward to reverse, or vice versa, while the vehicle is still in motion, and when the accelerator is depressed, the transmission and torque converter act as a brake, bringing the vehicle to an abrupt stop before moving in the opposite direction. The shock load on the transmission and torque converter, due to the sudden braking and reversing direction is extremely hard on the mechanism, and results in frequent, expensive repair jobs. The owners of the fork lifts are vexed by the constant expense of repairs and the inconvenience of down-time, while the fork lift is out of service, but the fork lift operators, who are primarily concerned with maneuvering their vehicles at top speed so as to get the work done, find it expedient and convenient to shift gears in the manner described. Thus, the fork lift owner finds it difficult to get the cooperation of the operators in driving the vehicles as they should be driven, i.e., by applying the brakes and bringing the vehicle to a stop before shifting gears.
Another problem with fork lift trucks is that they sometimes have a tendency to slip out of gear from low to neutral while running down a steep grade with a large load, using the engine drag to slow the vehicle and keep everything under control. When this happens, the fork lift loses the braking action of the engine and suddently lurches downhill, completely out of control. The operator may be killed or injured when this happens, while the least-serious outcome may be a spilled load and a toppled fork lift.
Still another problem with fork lifts is that if one is left standing unattended with the gears in neutral while the engine is idling, vibration will sometimes cause the transmission to slip into gear, so that the vehicle starts moving off with no one at the controls. This can result in serious damage and/or injuries.